The data published here are the input for the report "Clay mineral inventory in soils of Europe based on LUCAS 2015 survey soil samples" (2024), which describes them in detail.
From the report, we quote the abstract and the conclusions.
Abstract
Clay minerals are a key factor in mineral soils as they are controlling physic, chemical and biological soil properties. The X-ray diffraction (XRD) analysis has been widely used to identify and quantify minerals in earth science The aim of this research is to describe the clay minerals in soils of Europe and United Kingdom by using soil samples from the Land Use/Cover Area Frame Survey (LUCAS) topsoil database sampled in 2015.
A subset of 388 soil samples were selected from LUCAS 2015 topsoil survey. The clay fraction (<2 μm) was separated by sedimentation in distilled water. X-ray powder diffraction (XRPD) measurements have been carried out with a Siemens D5000 diffractometer with a graphite monochromator, using CuKα radiation at 40 kV and 40 mA. Clay mineralogy has been studied by measurement of basal spacing parameters on the clay fraction oriented in glass slides: 3 to 13 °2θ range 0.02 °2θ step size.
The study involved the measurement of the 1. air-dried sample, 2. ethylene glycol solvated sample, 3. heat treatment at 110, 350 and 550 °C. Identification of clay minerals were based on the d-spacing value of their 00l (mainly 001) reflections after different diagnostic treatment. The semiquantitative composition of <2 μm fractions was estimated by using integrated areas of 00l reflections.
Brief description of the clay mineralogy of all samples and semi quantitative mineral composition was performed at country level. The X-ray diffractograms after the different treatment (black = untreated, blue = ethylene glycol solvated, green = 110 °C, dark red = 350 °C, red = 550 °C) for each soil sample were analyzed. Majority clay minerals were compared to soils properties such as CEC, soil pH, soil organic carbon (SOC), and clay and sand content. Current descriptive analysis can be used to identify the most relevant clay minerals in soils of Europe.
Monitoring over time can be used as soil health indicator to establish potential correlations between clay
minerals and relevant threats as soil degradation, soil erosion, and soil pollution.
Conclusions
From the point of view of clay mineralogy and general mineralogy:
A wide variety of soils have been analysed for clay mineralogy in UE and United Kingdom countries. As has been stated above, in general, clay content and the presence of permanent charged minerals conditioned, in this order, the CEC values of soils rather than pH or OM contents.
On a qualitative observation basis, central Europe (i.e. Germany, Czechia, Poland) and northern countries (i.e. Finland, Sweden, Latvia) have clay mineralogies more akin to have chlorite-like or vermiculitic compositions in addition to the persistent predominance of illite. These mineralogies are consistent with highly weathered, organic rich, topsoils form more cold and humid regions, very poor, on the other hand, in clay minerals, and in
nutrients such as calcium, magnesium and, potassium.
Kaolinite and smectite are more represented in mediterranean or southern UE countries and, in addition, iron oxyhydroxides are present and differentiate orange-brown colours of these regions.
Quartz is the main stable no clay mineral and feldspars or amphiboles appear in soil mineralogies from the well-known granitic shields of Scandinavian countries.
Presence and quantification of sparingly soluble (carbonates) or soluble minerals (gypsum and halite) is not always stablished with certainty or either quantified, it is necessary to revisite some samples to capture signal overlapping in order to obtain further interpretations on salinity issues. Knowledge of the existence of lime additions to analyzed soils will be important to solve some of the interpretations concerning calcite presence or
not in representative soils.
Current descriptive analysis can be used to identify the most relevant clay minerals in soils of Europe. Monitoring over time can be used as soil health indicator to establish potential correlations between clay minerals and relevant threats as soil degradation, soil erosion, and soil pollution.
The data
The data come as diffractograms. (a number of .dat files per sample) and an Excel file that contains a number of properties per sample, and a shapefile that indicates the position of the samples.
Diffractograms: all datafiles for 383 samples have been zipped into one file.
The Excel file: contains
- the field Point_ID contains the official and unique LUCAS point ID
- the field 'Sample ID' allows to find the corresponding data Diffractogram data files
- the fields 'S' to 'Wed' are explained in the report on p 58 in the list of abbrevations
The Shapefile contains all locations of the 383 analyzed samples; the attribute table contains the Point_ID for the location and also the theoretical LUCAS coordinates to which the samples refer.
